1. Field of the Invention:
The present invention relates to a method for cleaning filter candles of a candle filter using a cleaning fluid which is in-flowing from the filtrate side into the interior of the candle, which cleaning fluid is pressed through the filter candle, in the direction opposite to the filtrate direction, by means of a gaseous medium under an overpressure, from the interior to the exterior, as well as to apparatus for carrying out such method.
2. Background Information:
In a known method of cleaning filter equipment, the filter cake produced at the filter on the side of the un-filtrate of the filter equipment is removed thereby that the interior space at the inlet-side, as well as part of the filtrate space positioned above the inlet-side interior space, when the exit-side is closed, is filled with water from the un-filtrate side, whereby the air positioned above the water is compressed in the filtrate space. Upon filling in of the water and compression of the air in the upper space of the filtrate space, a discharge is opened all of a sudden on the un-filterated side such that the air under pressure causes an intense back-flow of the water present in the filtrate space, through the filter, and thereby the filter cake accumulated on the un-filtrate side of the filter is removed from the filter, and is mixed with the water present in the un-filtrate space, and with this is removed through the drain from the filter equipment.
This method is rather simple but has the decisive disadvantage which is to be seen therein that the filter cake removed from the filter is mixed with such a volume of water which is nearly equal to the total volume of both interior spaces of the filtering equipment. Since this water which includes the filter cake can not be passed to sewage in this condition, subsequently a laborious separation of the sludge from the water is necessary. This is the cause of high equipment costs and not insignificant operating costs.
In a further known method for cleaning filtering equipment with installed filter, a cleaning fluid is brought to an overpressure, in a separate container, and for carrying out the cleaning, is brought, via an inlet conduit, to the removal-side of the filter equipment, and from there is pressed through the filter in the direction opposite to the direction of filtration. For moving the cleaning fluid from the accumulated (or special, separate) container to the filtering equipment, a gaseous medium under overpressure is used.
As cleaning medium, usefully, water is employed and as gaseous medium air is used. For distribution of the cleaning fluid serve, respectively at the removal-side candle end arranged nozzle-shaped constrictions, or at a distance from such constriction in the candle interior arranged impact bodies, with which the in-flowing cleaning fluid is deflected to all sides in the direction of the interior walls of the candles.
In other words, nozzle-shaped constrictions are arranged at that end of a candle which is at the filtrate removal side, for distribution of the cleaning fluid. Alternatively, at a distance away from such constrictions are arranged impact bodies for deflection of cleaning fluid.
This has the disadvantage that the nozzle-shaped constrictions are present for the introduction of the cleaning fluid into the interior of the filter candle, as well as for the air under pressure, such that on termination of a pressure impulse, a post-flow, or, in other words, a trailing or tailing type of flow behavior, of cleaning fluid is not possible.
In German Laid Open Patent Application No. 2 227 821 there is disclosed a method comprising the steps of emptying the portion or compartment receiving liquid to be filtered and replacing the emptied volume or space with a pressurizing gas acting in the direction opposite to the pressure in the filter elements and the compartment or portion receiving filtered liquid.
In German Laid Open Patent Application 195 18 575 A1 there is disclosed an extension element of the filter candle, which element extends into the filtrate compartment. Water under pressure of cleaning air is then forced through the extension element and the filter candles.
U.S. Pat. No. 5,437,788 to S. A. Geibel et al. is concerned with a filter assembly comprising: a housing divided into a first chamber and a second chamber, the second chamber being arranged to contain a backwash liquid; a filter element disposed in the first chamber and having an interior; a conduit disposed in the second chamber and having an interior which communicates with the interior of the filter element and an opening which communicates with the second chamber; a weep hole arranged to drain backwash liquid from the second chamber into the filter element or the conduit, the weep hole being below the opening in the conduit; and a gas feed pipe arranged to introduce pressurized gas into the second chamber to force the backwash liquid through the conduit and into the filter element.
In other words, this invention is concerned in one aspect with cleaning of tubular filter candles or elements of a tubular filter arrangement, in which vertical tubes or cartridges, i.e., candles, are supported by a filtrate-chamber tube sheet in a vertical cylindrical vessel, compare pages 18-92 and 18-93 in Liquid-Solid Operations and Equipment in PERRY""S CHEMICAL ENGINEERS"" HANDBOOK, Seventh Edition, Robert H. Perry and Don W. Green, 1997, The McGraw-Hill Companies, Inc., ISBN 0-07-049841-5, incorporated herein by reference.
Also in other words, in filtration is achieved the separation of two phases, particulate form, i.e., solid particles or liquid droplets in suspension, and continuous, i.e., liquid or gas, from a mixture, herein also referred to as un-filtrate or liquid to be filtered, by passing the mixture through a porous medium. This may be cylindrical element filters, often referred to as candle filters, in which cylindrical elements or sleeves are mounted vertically and suspended from a header sheet, which divides the filter vessel into two separate compartments. The advantage of candle filters is that as the cake grows on the tubular elements the filtration area increases and the thickness of a given volume of cake is therefore less than it would be on a flat element, compare Filtration in Volume 10 of KIRK-OTHMER, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Fourth Edition, Jacqueline I. Kroschwitz; editor, 1993, John Wiley and Sons, Inc., ISBN 0-471-52679-9 (v. 10), also incorporate herein by reference.
The object of the invention resides here therein to find an improved solution with which it is possible, despite introduction of the gaseous medium under pressure, that there is achieved, at all times, an automatic post-flow of the cleaning fluid into the candle interior, so that, in a practical manner, constantly an impacting of the interior of the candle with this cleaning fluid can be assured.
In other words, there is established in accordance with one object a substantially automatic and effective flow of the cleaning liquid or fluid, including post-flow or tailing or trailing behavior thereof, so as to provide for enhanced removal of filter cake.
Another object resides therein to ensure that a continuously effective layer or sheet or film of cleaning liquid is provided at the interior surface of filter candles so as to assure a more rapid and improved removal of filter cake adhering to a filter element or candle, using an efficient volume of cleaning liquid.
The present invention teaches that these objects can be accomplished by a method thereby that the cleaning fluid and the gaseous medium are introduced into the interior of the filter candle through stream paths which are separate from one another.
In other words, a gaseous medium and cleaning fluid are flowed through the candle, but through separate passages, in the direction opposite to the direction of flow of the suspension or liquid which is to be filtered.
Thereby it was found useful in independent configuration of the invention that under maintenance of the cleaning liquid introduction, a constant fluid film is obtained, and this can be impacted by pulsating introduction of pressurizing gas.
In an advantageous embodiment of the method with pulsating pressurizing gas introduction it is contemplated that the time-wise intervals of pulsating pressurizing gas introduction correspond at least to the time-wise building-up of a fluid film which again impacts the interior wall, respectively, the pulsating pressurizing gas introduction is only then commenced as soon as at the interior wall of the candle there has been formed a fluid film extending over the full length.
The invention further relates to a filtering arrangement with back-washing capability with a separation plane, between the un-filtrate space and the filtrate space, and filter candles held therein with their upper ends, with the interior space thereof being disposed so as to have the forward opening extend into the filtrate space, whereby the forward opening has two openings which are separate from one another, and which with respect to height terminate at different levels.
In an independent embodiment of the filter arrangement with back-washing capability it is contemplated that the forward opening of the filter candle has an inlet-line for cleaning fluid and, separate with respect to the inlet-line and at a higher plane terminating, a second inlet-line for a gaseous medium under pressure.
As useful embodiment of the filter arrangement with back-wash capability it is contemplated that the inlet-line for cleaning fluid is configured as annular gap which, on the one hand, is formed by the interior wall of the filter candle and, on the other hand, by a pipe piece which is provided for the introduction of a gaseous medium, and this pipe piece is terminating above the filter candle and/or the annular gap.
With the method in accordance with the invention and the for this configured filter arrangement with back-wash capability, it is ensured that in practical manner a constant fluid film can flow from the filtrate space into the interior of the filter candles, and in this manner a closed fluid film is formed at their interior walls, which achieves, on impacting with pressure, a uniform and assured removal of the filter cake. Particularly when employing a pulsation pressure impacting there can, within a short period of time, the for the cleaning provided fluid film be built up in the interior of a candle, whereby there is accomplished a substantially more
One feature of the invention resides broadly in a method of operating a plant in which containers are filled with liquid, said method comprising the steps of:
(a) moving containers to a filling machine;
(b) filling said containers with liquid when filtered;
(c) removing filled containers from said filling machine, said filtered liquid being produced by
(d) providing a liquid to be filtered in a first batch to a filter apparatus having candle filter elements, at least a portion for receiving liquid to be filtered, and a portion for receiving liquid when filtered;
(e) moving said first batch of said liquid to be filtered in a first direction from a first surface to a second surface of said candle filter elements, from said portion receiving liquid to be filtered, through said candle filter elements and thereby collecting solids at said first surface of said candle filter elements as filter cake;
(f) terminating filtering according to Steps (d) and (e);
(g) intiating flow of a cleaning liquid along a first flow path, over said second surface, for inducing removal of filter cake from said candle filter elements by flowing a sheet of cleaning liquid over said second surface;
(h) pressurizing and directing a flow of gaseous medium in a second flow path separate from said first flow path to force said sheet of cleaning liquid flowing on said second surface through said candle filter elements from said second surface to said first surface, to thus dislodge said filter cake on said first surface;
(i) removing said filter cake from said candle filter elements by the interaction of cleaning liquid and gaseous medium;
(j) terminating cleaning according to Steps (g), (h) and (i); and
(k) moving a second batch of liquid in said first direction through said candle filter elements.
Another feature of the invention resides broadly in a plant in which containers are filled with liquid, comprising: apparatus for moving containers to a filling machine; a machine for filling said containers with liquid when filtered;
apparatus for removing filled containers from said filling machine, said filtered liquid being procured by apparatus for providing a liquid to be filtered in a first batch to a filter apparatus having candle filter elements, at least a portion for receiving liquid to be filtered, and a portion for receiving liquid when filtered;
apparatus for moving said first batch of said liquid to be filtered in a first direction from a first surface to a second surface of said candle filter elements, from said portion receiving liquid to be filtered, through said candle filter elements and thereby collecting solids at said first surface of said candle filter elements as filter cake;
apparatus for terminating filtering by said filter apparatus;
apparatus for initiating flow of a cleaning liquid along a first flow path, over said second surface, for inducing removal of filter cake from said candle filter elements by flowing a sheet of cleaning liquid over said second surface;
apparatus for pressurizing and directing a flow of gaseous medium in a second flow path separate from said first flow path to force said cleaning liquid flowing on said second surface through said candle filter elements from said second surface to said first surface, to thus dislodge said filter cake on said first surface;
apparatus for removing said filter cake from said candle filter elements by the interaction of cleaning liquid and gaseous medium;
apparatus for terminating operation of said apparatus for initiating flow of a cleaning liquid, said apparatus for pressurizing, and said filter cake removal apparatus; and
apparatus for moving a second batch of liquid in said first direction through said candle filter elements.
Yet another feature of the invention resides broadly in a method of operating and cleaning filter apparatus having filter elements, at least a portion for receiving a liquid having solids suspended therein, and a portion for receiving liquid when filtered, said method comprising the steps of:
(a) moving a first batch of said liquid having solids suspended therein in a first direction from said portion for receiving a liquid having solids suspended therein through said filter elements from a first surface to a second surface of said filter elements and thereby collecting solids at said first surface of said filter elements as filter cake;
(b) terminating filtering according to Step (a);
(c) initiating flow of a cleaning liquid along a first flow path, over said second surface of said filter elements, for inducing removal of filter cake from said filter elements by a flowing layer of cleaning liquid;
(d) pressurizing and directing a flow of gaseous medium in a second flow path separate from said first flow path to force said cleaning liquid passing over said second surface to permeate from said second surface to said first surface of said filter elements and to thus dislodge said filter cake on said first surface of said filter elements;
(e) terminating cleaning according to Steps (c) and (d);
(f) removing said filter cake obtained by said filter elements through interaction of cleaning liquid and gaseous medium; and
(g) moving a second batch of suspension in said first direction through said filter elements.
Still another feature of the invention resides broadly in a plant operating and cleaning filter apparatus having filter elements, at least a portion for receiving a liquid having solids suspended therein, and a portion for receiving liquid when filtered, comprising:
apparatus for moving a first batch of said liquid having solids suspended therein in a first direction from said portion for receiving a liquid having solids suspended therein through said filter elements from a first surface to a second surface of said filter elements and thereby collecting solids at said first surface of said filter elements as filter cake;
apparatus for terminating filtering by said apparatus for moving a first batch of said liquid having solids suspended therein;
apparatus for initiating flow of a cleaning liquid along a first flow path, over said second surface of said filter elements, for inducing removal of filter cake from said filter elements by a flowing layer of cleaning liquid;
apparatus for pressurizing and directing a flow of gaseous medium in a second flow path separate from said first flow path to force said cleaning liquid passing over said second surface to permeate from said second surface to said first surface of said filter elements and to thus dislodge said filter cake on said first surface of said filter elements;
apparatus for terminating action of said initiating flow of cleaning liquid and said apparatus for pressurizing and directing flow of gaseous medium;
apparatus for removing filter cake from said filter elements by interaction of cleaning liquid and gaseous medium; and
apparatus for moving a second batch of suspension in said first direction through said filter elements.
A further feature of the invention resides broadly in the method for operating and cleaning filter apparatus having filter candles, a portion for receiving a liquid to be filtered, and a portion for receiving liquid when filtered, in cyclical manner, said method comprising the steps of:
(a) introducing said liquid to be filtered in a first direction for filtering solids from said liquid;
(b) building-up filter cake at said filter candles to a predetermined level on a first surface of said filter candles;
(c) by flowing a sheet of cleaning liquid in a first path over a second surface of said filter candles in the direction opposite to said first direction through said filter candles for removal of said filter cake adhered in Step (b), for initiating removal of filter cake;
(d) passing a gaseous medium, in a second path separate from said first path, under sufficient pressure along said flow path of cleaning liquid to ensure effective back-washing of filter cake from said filter candles; and
(e) removing dislodged filter cake and cleaning liquid.
Another feature of the invention resided broadly in the filter apparatus including back-washing capability, comprising:
a filter vessel having a portion for receiving a liquid to be filtered, a portion for receiving liquid when filtered, and at least one filter element, said at least one filter element having a first surface for collecting solids as filter cake and a second surface opposite from said first surface;
control apparatus, operatively connected to said filter vessel to control formation of a flowing layer of cleaning liquid at said at least one filter element and to control pressurizing said layer with gaseous medium under pressure;
apparatus, operatively connected to said filter vessel and said control apparatus, for flowing said layer of cleaning liquid along said second surface of said at least one filter element; and
apparatus, connected to said control apparatus and configured to interact with said control apparatus, for directing said gaseous medium under pressure separately from said cleaning liquid to apply a pressure on said second surface of said at least one filter element, to act upon said cleaning liquid on said second surface to permeate said cleaning liquid through said at least one filter element, to thus remove filter cake on said first surface of said at least one filter element.
The above-discussed embodiments of the present invention will be described further hereinbelow with reference to the accompanying figures. When the word xe2x80x9cinventionxe2x80x9d is used in this specification, the word xe2x80x9cinventionxe2x80x9d includes xe2x80x9cinventionsxe2x80x9d, that is, the plural of xe2x80x9cinventionxe2x80x9d. By stating xe2x80x9cinventionxe2x80x9d, the Applicants do not in any way admit that the present application does not include more than one patentably and non-obviously distinct invention, and maintain that this application may include more than one patentably and non-obviously distinct invention. The Applicants hereby assert that the disclosure of this application may include more than one invention, that these inventions may be patentable and non-obvious one with respect to the other.